Arm resonance - the anal way

borchee

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#1
OK, guys...here it goes!

The goal of this thread is to choose a cartridge to match an arm from a complete newbie standpoint.

To make things "easier", let's go with:
- tonearm is SME 309 (thanks Bob Boyer)
- looking at two cartidges; Ortofon 2M Black and audio-technica VM760SLC.

I went with this particular arm and cartridges, simply because there are datasheets available.

Now...Ortofon has the formula to calculate the resonance frequency, I have the data required (arm's effective mass and cartridge compliance), so nothing can be more straightforward...untill I start reading:
- "When selecting either MC or MM cartridges for your record player, total effective mass of tonearm (including cartridge and headshell) has to be taken into account in relation to the mechanical compliance (elasticity) of the cartridge cantilever system."
- "M - Total tonearm system mass which is a sum of Mass of cartridge, Mass of headshell and screws and Effective mass of tone arm (all values in gram).".

PREDICAMENT no. 1
Total effective mass....total tonearm mass...eeeehm?...what now?! OK, let's read-up on effective mass............done and understood - it's about the moment of inertia. Fine?....nope, not by far, if the accuracy level is supposed to be according to stated PI-value (to the ELEVENTH decimal). OK, let's go anal then. You can't just add mass of an object to effective mass! This might be accurate/negligible enough, but I can't tell - remember the PI-value...which leads to

PREDICAMENT no. 2
I can make an educated guess about the effective mass/moment of inertia of the cartridge + mounting screws (with SME 309 the headshell is a part of the arm) with a higher accuracy than simply assuming this mass (with dimension of zero) is concentrated on the tip of the stylus...which leads to

PREDICAMENT no. 3
The effective mass, as stated by SME...based on what position of the counterweight?!

PREDICAMENT no. 4....
Compliance (dynamic) of the audio-technica given at 100Hz (that's why I have chosen it) - how does it translate to 10Hz...and does the formula relate to 0, 10, 100Hz or whatever value?

And so on and so forth.

Take it from here.

Anyways, merry Christmas and a happy new year.
Borut
 

J!m

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#2
Compliance has to be calculated to a common unit.

I went through that when dealing with the output of my HOMC Benz-Micro Silver. Written totally differently that A-T MM spec, but nearly identical output once calculated.
 

borchee

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#7
....bearings have zero (0) resistance...
Being anal about being anal - well done!!! This is another example of what we should not be requiered to think of - it should be included in manufacturer's specs.

An arm suspended on a "string", with magnetic balance, should exclude it...please, don't get into "torsional-stiffness" of any kind of a string.
 

NeverSatisfied

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#10
This is probably why low mass arms and high compliance carts faded in popularity.
You need a physics degree, bat ears and the luck of the Irish to get it all setup right. Like the idiot I am, I decided to go down this road without any of the above.
My solution….follow the path of others and some trial and error, after all, “it’s the journey not the the destination”. At least that’s what I keep telling myself, lol.
 

borchee

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#11
….follow the path of others and some trial and error...
Sure, but there is no consensus about, well, pretty much everything about HiFi. I have an arm and I want a new cartridge - as much as I enjoy the trial-and-error-method, it can get expensive in a hurry. I know I can change the effective mass/resonance frequency with a "classical" arm by "simply" altering the counterweight's either dimensions/shape and/or mass...or material used. With data about the existing counterweight, I can even juggle some numbers to get where I want to. But why?!
 

NeverSatisfied

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#12
Simply for the joy……for some the joy is just the music, for others the joy is the challenge and for many it might be combinations, it doesn’t matter why we choose these things, only that we get and give joy from our endeavors.
For me, even though I don’t understand much of what is being discussed here, I really enjoy being exposed to the thoughts and insights of other people with the same love and enthusiasm for all things audio as I do.
Keep it coming my friend, it is all golden.
 

8991XJ

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#14
Going anal about arm resonance is a waste of grey matter. Since we know what the resonance for a playback system should be to avoid issues, 5-14 Hz or so then just slap a damn cartridge into the tonearm, drop the nail on a vinyl and give it a spin. Since my records are generally flat I worry even less about the low end of that resonance frequency.

We can discuss this all day long but without the tools needed to determine the resonance frequency, those Japanese cartridges with 100Hz numbers are not helping those anal enough to demand a resonant frequency of 8.5-10.5 Hz. Folks that have the records that can determine resonant frequency don't seem to post what they find out about those cartridges enough for us to use the 100 Hz numbers properly. I have read a conversion factor of 1.2-2.0 a pretty wide range, making most of those nails a good match with most tonearms.

Because of the wide range of more than acceptable resonance frequencies and the lack of compliance information on cartridges this is as much a conundrum as setting the antiskate. Lots of opinions and lots of right answers just because it is not a situation where only one answer is correct.
 

borchee

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#15
...even though I don’t understand much of what is being discussed here...
This is exactly what I'm trying to bring across - it shouldn't be requiered of you to know anything about the stuff discussed, but to fill the formula with numbers to check/assure your arm-cartridge-combo is within the desired frequency.

I can't comprehend how manufacturers are unable to provide the correct data. Surely SME has the means to measure or calculate the moment of inertia, the center of gravity and what not. So do Ortofon and audio-technica...along with compliance. Why are we forced into clearing the crap up by ourselves?!

@8991XJ, I agree, but how can I avoid an issue, If I'm not given the neccessities to do so.
Waste of grey matter...perhaps, but mine rather enjoys a challenge.
 

Makymak

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#17
Why are we forced into clearing the crap up by ourselves?!
See it differently. If a unique formula and unique equation was true, then every respected manufacturer would follow this exact formula. Not only on turntables but on everything that is involved with sound.

But sound is perceived differently among people. Maybe that's why there is such a polyphony on audio equipment designing. I believe that no one, even the manufacturers, can predict with absolute accuracy the sound their part would produce from the paper, without some kind of try and error. Show me all the factors you believe that contribute to the sound and I will show you just as many you didn't counted on.

I understand that my approach does not contribute to the thread subject. But my belief is that it's too hard to take control, identify and eliminate all the parameters acting on a sound system.

I sincerely support any attempt to distinguish the physics that take place on the tonearm system. It's a great exercise! And even if you can't reach to a complete perceiving of the whole thing, it's a good opportunity to learn something more! This is the way I stand up for!
 
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derek92994

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#19
Lost me at the first post, pretty much all carts I own work on all arms I own. I have never had a cart/arm combo sound ‘bad’ Whats this resonance thing? What is high compliance and low compliance for arms and carts?
 
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Makymak

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#20
As what I understand (not being an expert) in plain words:

High compliance cart means that the stylus is more free to travel up and down due to a softer suspension. So, if this cart is attached on a heavy arm, any warping of the vinyl will make the stylus absorb the most energy since it will be more difficult to move the heavy arm. As long as it's suspension is soft, absorbing this energy will lead the stylus to travel further into it's shell beyond it's effective limits leading to sound degradation and some other ill-effects. The most important effect is that this big stylus' travel in conjunction with the heavy mass will trigger a resonance that is undesired.

On the other hand, a low compliance cart's stylus have a stiff suspension so it can't track accurately the vinyl and needs some extra "stabilization" to keep on tracking. This should applied by the inertia of the tonearm's mass. If such a cart is mounted on a low mass arm then there will be no sufficient inertia to track correctly the groves. See what happens, the groove walls push the stylus. The stylus pushes the cantilever. The cantilever pushes the magnetic element into the effective coil's field so the coils produce the current it drives the amp. If the inertia of the tonearm isn't sufficient, the cantilever won't move the magnetic element but will move the whole tonearm since arm's resistance in moving is smaller due to the small inertia.

Please correct me if I am wrong!
 
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